Frequency control by electronic counter chains



Sept. 12, 1950 l. E. GRosDol-'F 2,521,789

FREQUENCY CONTROL BY ELECTRONIC COUNTER CHAINS Filed Feb. 25, 1948 2 Sheets-Sheet;

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@4f V y' jl'yz ATTORNEY Sept. 12, 1950 l. E. GRosDoFF 2,521,789

FREQUENCY CONTROL BY ELECTRONIC COUNTER CHAINS Filed Feb. 25, 1948 2 sheets-sheet 2 @NNN imm INVENTOR BUR E. ERIJSdnff ATTORNEY Patented Sept. 12, 1950 FREQUENCY CONTROL BY ELECTRONIC COUNTER CHAINS Igor E. Grosdo", Princeton, N. J., assigner to Radio Corporation of America., a corporation of Delaware Application February 25, 1948, Serial No. 10,665

(Cl. Z50-$6) Claims. 1 This invention relates to automatic frequency control systems such as are adapted to maintain a predetermined relation between the out-- put frequencies of a variable frequency generator and aconstant or standard frequency generator. Heretofore there havebeen proposed automatic frequency control systems wherein the output` frequency of a variable frequency generator is regulated with crystal accuracy and at different values by comparing two series of pulses having substantially the saine frequency. One of these series of pulses is supplied from a constant,

frequency generator through a frequency divider having a Xed division ratio. The other of these series of pulses is supplied from the variable frequency generator through a frequency divider which is adjusted so that its output frequency."

is substantially equal to that of the fixed frequency divider. These two substantially equal frequencies are applied to a detector, such as a phase comparator or the like, which controls the reactance tube or other frequency determining-y element of the variable frequency generator in such a way as to maintain the frequency of the variable frequency generator substantially constant at any one of its adjustedvalues. Automatic frequency control systems of this type are disclosed in the copending applications of Charles J. Young, Ser. No. 719,035, filed December 28, 1946, issued as Patent No. 2,490,500 on December 6, 1948, and John D. Woodward, Ser. No. 743,234,

filed April 23, 1947, issued as Patent No. 2,490,499`

on December 6, 1949. The details of the variable frequency generator are disclosed in a copending application of Olin L. MacSorley, Ser. No. 743,- 266, filed April 23, 194'?.

The present invention accomplishes the samev result as the systems of the aforesaid applications of Young and Woodward but differs from those systems in that the fixed and-adjustable frequency dividers of those systems are replaced by a single frequency divider. To this single frequency divider, the outputs of the fixed and variable frequency generators are applied alternately in such a way as to produce at the output of the frequency divider a square wave from which a unidirectional 'component is extracted `similar systems heretofore available.

ating cycle of the frequency divider under the particular condition established by its control circuits.

The principal object of the invention is to provide an improved automatic frequency control system and method of operation which involve fewer parts and is of simpler construction than the Important objects of the invention are (1) the provision of a frequency divider provided with control circuits such that it presents one capacity to input pulses of one frequency and another capacty to input pulses of another frequency, and (2) the provision Yof a frequency divider with means for alternately selecting output pulses from different sources.

The invention will be better understood from the following description'considered in connection with the accompanying drawings and its scope is indicated by the appended claims.

' Referring to the drawings: f

Fig. 1 is a boxldiagram of a first form of the i invention whereinv the pulses from the fixed and variable vfrequency generators are alternately 25 supplied to adjustable parts of the output section of the frequency divider through switches each arranged to select any desired number of stages of the frequency divider. 'Under these conditions, there is presented to each of the generators a frequency divider capacity which is determined by the position of the switch to which it is connected.

Fig. 2 is a box diagram illustrating a second form of the invention wherein the output pulses of the two generators are applied alternately to the input of the frequency divider and are delivered from the frequency divider through switches capable of adjusting the frequency divider to produce different division ratios or capacities. This form of the invention also includes means for automatically resetting the frequency divider to its zero or standby condition at the end of each group of pulses delivered from each of the generators.

Fig. 3 is a box diagram illustrating a third form of the invention wherein the output pulses of the two generators are supplied alternately -to the input of the frequency divider and are delivered at the output of the frequency divider. In this form of the invention, the two frequency divider capacities or division ratios are controlled "another control pulse.

divider is split into separate sections each of which has an adjustable capacity. In this form of the invention, the output pulses of the two generators are alternately supplied to an adjustable number of stages at the output ends of `the frequency divider sections.

Fig. 5 is a wiring diagram including switches which may be manually operated to put the autornatic frequency control system into the form of Fig. 2 or Fig. 3. With these manually operated switches positioned as in Fig. 5, the system is in the form of Fig. 2.

It will be noted that each of the four modifications of the invention include a frequency divider 24 having means for changing its capacity so that its cycle of operation is completed in response to any selected number of input pulses delivered from a constant frequency generator f 25 through a gate 2S or from a variable frequency 'generator 21 through a gate 28. The term gate is used herein to indicate any device which conducts pulses in response to one control potential and is made nonconductive inresponse to It may be a multi-grid vacuum tube to one control grid of which are applied the pulses and to another control grid of which are applied the control potentials.

The frequency divider is preferably of the type wherein a plurality of trigger circuits are connected in cascade. The details of such a freiquency divider are shown in the central part of Fig. 5 and its various characteristics are disy cussed in connection with this figure.

fxed contact members 3G. Similarly, the switch 3B includes a movable contact member 39 adapted t4 in Fig. 3, and (4) as switches successively to engage a series of fixed contact finembers 49. Thefxed contact members 3.8 and 4D are connected to leads corresponding to the anode leads 16 to 11 of Fig. 5.

By suitable positioning of the switch member 31', the frequency divider 24 may be made to complete its cycle of operation in response'to any desired number of pulses applied to it from the v"generator 25 through the gate 25. In the same manner the switch 3i] is effective to make the frequency changer 214 complete its cycle of operation in response to any desired number of pulses applied to it from the generator 21 through the gate 28. f

' Each time the frequency divider 24 completes its cycle of operation, a negative pulse is applied from it to a trigger circuit 4l which may be similar to the trigger circuit VI of Fig. 5. The trigger circuit 4I is so connected to the gates 26 and 28 that these gates are never both open or closed at the same time. '4| in one of its stable operating conditions, a vpositive potential is applied through a lead 42 to Thus with the trigger circuit open the gate 25 and a negative pulse is applied through a lead 43 to close the gate 28. When the trigger circuit 4l is in its other stable operating condition, the potentials of the leads 42 and 43 are reversed, the gate 26 is closed and the gate 28 is open.

When the trigger circuit 4l is in one of its sta- Y ble operating conditions, a positive potential is "applied from it to a detector 44. When the trigger circuit 4I is in the other of its stable operat- 4 ing conditions a negative potential is applied from it to the detector 44.

Thus the connections may be such that (1) a negative potential is applied to the detector 44 while pulses are supplied from the generator 25 through the gate 25 and the switch 29 to the frequency divider 24 and (2) a positive potential is applied to the detector 44 while pulses are supplied from the generator 21 through the gate 28 and the switch 3Q to the frequency divider 24.

It is easy to see that the positive potential Aapplied. to the detector 44 is in the form of a square wave covering a time interval dependent on the frequency of the pulses delivered from the generator 21. Thus, if the frequency of the generator 21 tends to increase, the period of the square wave is shortened and vice versa. The time interval between the positive square waves is constant for the reason that the output frequency of the generator 25 is constant. The positive square waves are detected by the detector'44 and applied through a lead 45 to the frequency control element of the generator 21 in such a way as to maintain a substantially constant relation between the output frequencies of the two generators.

Thus assuming that the capacity of the frequency divider 24 is alternately changed with the frequencies of the pulses applied to it from the different generators, as explained above, the positive and nega-tive loops of the square wave f applied from the trigger circuit 4I to the detector 44 are the direct functions of the frequency divider capacities N1 and N2 and inverse functions yof the freqencies f1 and f2 of the generators Z5 where K is an arbitrary constant determining the level of the D.-C. component. It can be seen that, for K=I1 and N1=N2, f1 must be equal to .fi in order to obtain a symmetrical square Wave, and that any change in either frequency would destroy this symmetry. Also it can be seen that by changing N1 and N2 the same result is obtained. Therefore, Equation l can be rewritten which means that basically the ratio of the two capacities N1 and N2 of the frequency divider 24 must be the same as the ratio of the two frequencies f1 and f2 of the generators 25 and 21. It also means that, for any selected ratio il fz the capacity of the frequency divider must be changed from N1 and N2 and back again depending on which frequency is supplied tothe frequency divider. As explained above the changes in N1 and N2 are effected by the switches 29 and 30 and the selection of f1 and f2 are made by the gates 26 and 28 in response to operation of the trigger circuit 4|.

The switches 3l and 32 of Fig. 2 are of a type described in detail in connection with Fig. 5, They are so interconnected with the frequency changer 24 as (l) to adjust the two capacities ofthe frequency divider, and (2) to deliver an I ,output pulse to the trigger circuit 44 when either loperating cycle of the frequency changer is completed. Also at the end of eachoperating cycle, a control pulse is applied through a lead 46 to a reset device 41 by which the frequency changer -24 is reestablished in its zero or standby condition. The trigger circuit, in the case of Fig. 2, is .operated in a manner explained in connection with the trigger circuitV of Fig. 5. Otherwise, the operation of the form of the invention shown by Fig. 2 is the same as that of Fig. 1.

The mcdiiication of Fig. 3 is like that of Fig. 1

4with the exception that 1) pulses from the generators25 and 21 are applied to the first stage (as in the case of Fig. 2) and (2) the two capacback connections have been shown, it is apparent --that there will 'be provided as many such gates sand feedback connections as are required to accommodate the range of frequencies over which the generator 21 is to be operated.

The modification of Fig. 4.diifers from those of the preceding gures in that the frequency divider issplit into sections 24 and 24' between which is connected the gate 28 The switch 35 may :be like the switch 30 of Fig. l and the switch 36 .may be like the switch 29 of Fig. 1. Under these conditions, pulses are supplied alternately (1) from the generator 25 through the gate 26 and the switch 36 to the frequency divider section .2 45 and (2) from the generator 21 through the switch 35 the frequency divider section 24 and j the gate 28to the frequency divider section 24. .Each time'the section 24'v completes its operating cycle, a control pulse is applied to the trigger circuit 4| as indicated above and the section 24 is returned to its zero or standby condition. Sec- ,tion 24 likewise returns to its zero` or standby condition each time it completes its cycle of operation.

Assuming the generator 21 of Fig. 4 to be opl 4erating at a relatively highv frequency and the generator 25 to be operating at af relatively low frequency, the modification of Fig 4 has the ad- .vantage that the higher4 frequency is easily reduced to a value convenient for` operationA ofthe system. If the generator 25 is operating at the higher frequency, it shouldbe connected to the switch 35 and the generatori21 should be connected to the switch 36.

In the wiring diagranrof Fig. 5, the same references are used, insofar as is convenient, to indicate parts which correspond to parts of the preceding figures. The frequency divider 24 of Figs. 1 to 3 appears in Fig. 5 as four frequency divider sections. AThe :lirst section includes the trigger circuits VI to V4. The second, third and fourth sections are like the rst and are shown as boxes 83, 84 and 85. Bymeans of feedback connections 6I and 63, each sectionis adapted to reduce its input frequency inthe ratio of one to 10. Thus for each 10,000 pulses delivered through the yinputcapacitor I8 there could be delivered at the output capacitor 82 of the rst section 1000 pulses, at the output capacitor 86 of the second section 100 pulses, at the output capacitor 81 ,of vthe third section -10. pulses and atthe output capacitorSB of the fourth section l pulse( Otherwise stated, the frequency divider as illustrated by Fig. 5 is capable ofreducing the input `fr e- Y. quency in the ratio of `1 to 10,000.

` sistor.

The extent to whichthis frequency reducing capability is utilized isdependent (l) on the condition of theswitclfies 3l and 32 if the system is connected as illustrated'by Fig. `2 or (2) on the condition ofthe gates 33 and 34 in the feedback connections if the system is'connected as illustrated fby Fig. 3. '1 In Fig..5, the switch 3| of Fig. 2 is represented by the switches Si to S4 and thegates 9D, 84 and 104. The tube I I0 functions as apart ofthe reset device 41. The switch 32 of Fig. 2 has the same connections as the switch 3l and is shown as a box 409 and the selector switches S2 to S4'.

With the manually `operable Switches 48 to 50 open and the manually operable switches 5| to 54 closed as illustrated in Fig, 5, the system is connected as indicated in Fig. 2. With the switches 48 to 50 closed and the switches 5I to 54 open,

cathode grounded, (3) has bias potential applied y to its grid through a separate resistor, and (4) has operating potential applied to its anode through a separate resistor and a resistor which is common to the anodes of both triodes,

With these connections, only one of the triodes conduct current at a time. Current conduction is transferred from one to the other of the triodes in response (1) to the application of a negative pulse to the grid of a triode which is conducting, (2) to the applicationof a positive pulse to the grid of a triode which is not conducting or (3) to the application of a negative pulse to the lead A'through which thev separate anode resistors are `connected to the common anode resistor.

The selector switches Si to S4 for producing a desired control eifect in response to vdifferent numbers of pulses applied to the input ofthe different sections of the frequency divider is a three point switch which is moved over three series of fixed contacts which are each connected to a different anode of the section through a re- These connections between the anodes and the fixed contacts of the switch are so arv'ranged -thatthe switch delivers a positive control potential only in response to a number of The output terminals of the selector switches of the various sections are connected to a control circuit which functions to deliver a control potential only in response to the number of input 'pulses which is determined by the setting ofthe 'selector switches.

connected in tandem through coupling capacitors 26, 21 `and 28. Operating potential is applied to the anodes of the trigger circuits Vl to V4 respectively through common anode resistors 20 to 23. The anodes of the vdii'erent trigger circuits are indicated respectively by the reference numerals II and I2, I9 and I4, .I5 and i6 and I'I and I8. It will be noted that (l) the anode I of the trigger circuit V3 is coupled through a capacitor 62 anda resistor 53 to the right-hand grid of the trigger circuit V2 and (.2) the anode I'I of the trigger circuit V4 isrcoupled through a capacitor 5D and a resistor @I to the right-hand grid of the trigger circuit V3. In the standby condition of the section, current conducl tion isin the right-hand triode of each trigger circuit as indicated by arrows adjacent the separate anode resistors.

The operating cycle vof the section is indicated In this tabulation, .the number of applied input pulses is indicated by the numerals of the first column, the letter R indicates that current conduction is in the right triode of the trigger circuit, and the letter L indicates that current conduction is in the left triode of the .trigger circuit. It -will be noted that after the fourth input pulse V2 is turned back left when V3 turns left and that V3 is similarly turned left when V4 turns left.

The anodes II to I8 of the section are connected respectively through resistors 'It to 'I'I to the fixed contacts of a .selector switch Si. Movable contacts I8, 'I9 and 3.9 are arranged so that each moves along a different row of these fixed contacts. By comparing the arrangement of the iixed contacts with the above tabulation, itis easy to see that the most positive pulse is applied to the output lead 8| of the switch SI only when the number of input pulses applied to the decade corresponds to the switch position indicated by they numerals at the left-hand side ofthe fixed contacts.

Thus if the movable contacts I8 to 89 are in the 4 position, for example, the switch output .lead BI is connected to the anodes I2, I6 and I'I.

As shown by the tabulation, all these anodes are not conducting and at a relatively high positive potential at the count of 4. In the same way, the lead 8| is made more positive at the proper count for any other setting of the switch SI.

The decade Vl to V4 has its output couple-d through a'capacitor 82 to a similar decade 83. Subsequent decades 84 and 85 are similarly connected in tandem with the first two stages through capacitors 86 and 81. Additional decades may be likewise connected through a-capacitor 38.

The selector switch S2 is connected through a lead 89 to the output lead 8| of the selector SI and thence to the control grid of a pentode 99. The selector switches S3 and S4 ofthe decades 34 and 85 are connected through leads 9I and 92 and a common lead 93 to the control grid `of a pentode 94. l

Operating potential is applied from a lead 95 respectively through resistors 96 and 91 to the anodes 98 and 99 of the pentodes 90 and 94.

When a more positive potential is applied from all the selector switches SI to s4 to the grids of the pentodes 99 and 94, current is drawn through the resistors 96 and 91 and the potentials of the anodes 98 and 99 is made more negative. These anodes are connected to ground through separate resistors I and HlI anda common resistor H12 so that such more negative potential of the anodes is applied through a, resistor I 93 to the control grid of a pentode I04. Capacitors and I9@ may be connected in shunt to the resistors |90 and IDI for increasing the speed of operation.

When the grid potential of the pentode I04 is made more negative, less current is drawn through its anode resistor IO'I and a positive pulse is applied through the output lead Illa to the right hand grid of V5, and to the input lead 49 of the circuit by which the various sections are reset to their zero or standby condition.

The reset circuit includes a gas tetrode IIB which derives its operating potential from a lead II! through a. resistor II2.` The cathode and control grid of the tetrode IIB are connected respectively through a resistor II3 and a resistor H4 to a negative lead H5 through which bias potential is applied to the various grids of the sections.

c Connected between the anode and cathode of lthe tetrode Il!! in series with the resistor H3 is a capacitor I I6 which is charged during the normal non-conducting staterof the tetrode IIB. When the previously mentioned positive pulse is applied to the grid of the tetrode III] through the lead 46 and the switch 5l, the tetrode becomes conductive and the capacitor is discharged through the resistor II3. As a result, a positive pulse is applied to the reset lead III of the various sections which are thereby put into their standby condition. For normally setting the bias potentials applied to the decade grids a resistor I IB may be connected in the lead I I5 as indicated. i

The application of the positive potential from the anode of the tube |04 through the lead |08 and switch 56 to the left hand grid of the trigger circuit V5 (4I in Fig. 2) causes current conduction to be transferred from the anode 55 to the anode 5EV thus producing at this anode a morenegative potential which is applied through the lead 42 (1) to the gate 29 thereby interrupting the supply of pulses from the generator 25 and (2) to the second grids of the tubes 90 and 94 thereby rendering the switches SI to S4 ineiective to provide any potential which can aiect the operation of the reset tube IIll or that of the trigger circuit V5.

The transfer of current conduction from the anode 55 to the anode 56 also produces at the anode 55 a more positive potential which is applied through the lead 43 to the gate 28 and to the switch output control gate which corresponds to the tubes 90 and 94 and is contained in the box 199. As a result there are supplied from the generator 21 to the input capacitor I9 a number of pulses depending on the setting of the switch in the box |09 (this switch is like the switch SI) and on the settings of the switches S2 to S4.

When such number of pulses has been completed, a positive pulse (derived from the switch and switch control circuit which is the box IDB and has the same connections as SI and tubes 90, 94, IIJ4 and IIIl) is applied through a lead 55 and the switch 52 to the right hand grid of the trigger 9 circuit V5. As a result the gates 26 and 90-94 are opened as explained alcove and the gates associated with the generator 2l are closed so that pulses of a number dependent on the setting of the switches Sl to S4 are again delivered from the generator 26.

This cycle of operation continues so long as the setting of the selector switches is not changed. As a result, there is produced at the anode 55 of the trigger circuit V5 a potential of square wave shape. As previously explained, the time interval of the positive loop of this potential varies with change in the frequency of the -generator 2l and the negative loop of this potential has a constant time interval for the reason that the frequency of the generator is maintained constant. The positive loop is detected by the detector d4 and applied to the frequency control element of the generator 2l in a conventional manner to maintain a substantially constant ratio between the frequencies of the two generators.

In order to make the connections of Fig. 5 like those of Fig. 3, the switches 5l, 52, 55, 53, 54 and the corresponding feedback switches of the frequency divider sections 83, Sd and 85 (not shown) are opened, and the switches 50, 28, 49 and the corresponding feedback switches of the sections 83, 84 and 85 (not shown) are closed.

Under these conditions, the triode 34 and the corresponding triodes of the sections 83, 84 and 35 are made conductive when current conduction is in the anode 55 of the trigger circuit V5 and the triode 33 and the corresponding triodes of the sections 83, 84 and 85 are made conductive when current conduction is in the anode 55 of the trigger circuit V5. In this way the capacity of the frequency changer is made to alternate between two fixed values each time the frequency completes its cycle of operation and a negative pulse is applied through the capacitor 88 and the switch 56 to the trigger circuit V5. The gates 25 and 28 and the detector 'lli continue to operate as described above.

It is apparent that the feedback connections of the frequency divider may be other than those indicated and that suitable switching meansmay be provided for selecting such predetermined groups of the feedback connections as are required to accommodate different relations between the frequencies of the two generators.

What the invention provides is an improved automatic frequency control system wherein pulses from fixed and variable frequency sources are alternately supplied to a frequency divider which (1) is connected to have different division ratios for the pulses from the different sources and (2) functions to provide an output potential of square wave form having positive loops or halfcycles which have a time interval dependent on the frequency of the variable frequency source and are detected for maintaining a substantially constant relation between the frequencies of the two sources.

What is claimed is:

1. The combination of sources of fixed and controllable frequency, a frequency divider having an output lead, first and second division ratio selector means connected to said divider for adjusting the connections of said divider to divide said xed and controllable frequencies by divisors such that the resultant quotients are in the form of puises unequally spaced in time only as a result of slight variations in said controllable frequency, control means connected to said output lead and responsive to said pulses for alternately connecting said sources to said divider, and means connected to said controllable frequency source and responsive to an output potential of said control means for maintaining a substantially constant relation between said frequencies.

2. The combination of sources of xed and controllable frequency, a frequency divider having an output lead, first and second division ratio selector means connected to said divider for adjusting the connections of said divider to divide said xed and controllable frequencies by divisors such that the resultant quotients are in the form of pulses unequally spaced in time only as a result of slight variations in said controllable fref. quency, control means connected to said output lead and responsive to said pulses for alternately connecting said sources to said divider through said selector means, and means connected to said controllable frequency source and responsive to an output potential of said control means for maintaining a substantially constant relation between said frequencies.

3. The combination of sources of fixed and controllable frequency, a frequency divider having an output lead, first and second division ratio selector means connected to said divider for adjusting the connections of said divider to divide said fixed and controllable frequencies by divisors such that the resultant quotients are in the form of pulses unequally spaced in time only as a result of slight variations in said controllable frequency, control means connected to said output lead and responsive to said pulses for alternately connecting said sources to the input of said divider, and means connected to said controllable frequency source and responsive tol an output potential of said control means for maintaining a substantially constant relation between said frequencies.

4. The combination of sources of Xed and controllable frequency, a frequency divider having an output lead. iirst and second division ratio selector means connected to said divider for adjusting the connections of said divider to divide said fixed and controllable frequencies by divisors such that the resultant quotients are in the form .of pulses unequally spaced in time only as a result of slight variations in said controllable frequency, control means connected to said divider through said selector means and responsive to said pulses for alternately connecting said sources to the input of said divider, and means connected to said controllable frequency source and responsive to an output potential of said control means for maintaining a substantially constant relation between said frequencies.

5. The combination of sources of xed and controllable frequency, a frequency divider having an output lead, rst and second division ratio selector means connected to said divider for adjusting the connections of said divider to divide said xed and controllable frequencies by divisors such that the resultant quotients are in the form of pulses unequally spaced in time only as a result of slight variations in said controllable frequency, control means connected to said divider through said selector means and responsive to said pulses for alternately connecting said sources to the input of said divider, means connected to said controllable frequency source and responsive to an output potential of said control means for maintaining a substantially constant relation between said frequency, and means connected to respond to each of said pulses for resetting said divider.

IGOR E. GROSDOFF.

No references cited.y 

